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LONDON, England (CNN) -- Police investigating Thursday's attempted bombings on the London transit system have released images of four men caught on closed-circuit television at the incident sites around the time the attacks were attempted.

Authorities were urging the public to help find them.

Earlier Friday, authorities shot and killed a man at the Stockwell Underground station. Police said the man shot was not one of the photographed four men being sought.

Metropolitan Police Commissioner Ian Blair said, however, that the fatal shooting was "directly linked to the ongoing and expanding anti-terrorist operation."

Police said the man had emerged from a house that was under police observation, prompting surveillance officers to follow him to the Stockwell station.

It's in south London, one stop and about a mile away from Oval Station, one of the four bombing targets Thursday.

"His clothing and his behavior at the station added to their suspicions," a Scotland Yard statement said.

Witnesses said the man was rushing toward a subway when he was shot at around 10 a.m. (Full story)

Blair said any death is "deeply regrettable," but said the man refused to obey instructions to stop.

The shooting is a rarity in London, where police generally are not armed except for special response units.

The latest attacks came two weeks to the day 52 people were killed in four bombings targeting the city's mass transit.

As in the July 7 attacks, three subway trains and a double-decker bus were attacked, but in Thursday's case, the four homemade bombs stuffed in backpacks only "partially detonated," said Assistant Police Commissioner Andy Hayman. He noted that it was too early to determine how they went off.

Meanwhile, police announced an arrest in Stockwell in connection with Thursday's bombing attempts.

Police would not comment on whether the man arrested was one of the four men caught in the closed-circuit television videos.

Hayman said police searched three locations Friday, one of which was in West London. Scotland Yard identified the area further saying, "in West Kilburn, W9." Police cordoned off part of Harrow Road in that area.

It is not clear if one of the three locations mentioned includes the place of the arrest.

Police also arrested Friday a man at a rail station in Birmingham.

The Snow Hill station was evacuated and cordoned off, police said, and two suitcases were seized at the scene.

Images released

The first CCTV image released by police Friday showed a young man in a dark top with "New York" written on it apparently fleeing the Oval station in south London where a bomb was left on a train.

The second image showed a middle-aged man with a moustache wearing a gray T-shirt with a palm tree on it standing on the top deck of the number 26 bus in Hackney, east London.

The third image shows a man leaving Warren Street Underground station in central London at about 12:39 p.m. on Thursday. He was wearing dark clothes.

The fourth image showed a man at Westbourne Park Underground at 12:21 p.m. He later traveled west on the Hammersmith and City line to Shepherds Bush underground where he ran off. He was wearing a dark shirt and trousers, and was later wearing a white vest.

In other developments:

An east London mosque on Whitechapel Road said it received a bomb threat Friday. The mosque was evacuated, while police checked the building. People were then allowed back inside.

The mother of Germaine Lindsay, one of the July 7 bombers, said she grieves for the victims. Maryam McLeod told reporters on the island of Grenada she is convinced, however, that he was not involved. (Full story)